1. Field of the Invention
The invention relates to a composition for preparation of a hollow fiber porous membrane and a preparation method using the same. The hollow fiber porous membrane has high strength and large flux and the preparation method thereof involves melt spinning process.
2. Description of the Related Art
Conventional hollow fiber porous membranes and preparation methods thereof are well known to those skilled in the art. For example, hard elastic polymers, such as PP (polypropylene) and PE (polyethylene), are common materials to produce hollow fiber porous membrane. Specifically, PP as a bulk polymer is melted directly and treated using a spinning pack to yield a hollow fiber. Upon stability in structure, the hollow fiber is drawn and thus a microphase separation between the crystal region and the amorphous region therein happens, thereby resulting in the formation of a micropore structure. However, the resulting hollow fiber porous membrane has low porosity, poor hydrophilicity, and low water flux, mainly used for preparation of gas separation membrane, for example, artificial lung.
A method for producing a polyvinylidene difluoride porous membrane includes mixing a polyvinylidene difluoride resin and an organic liquid with an inorganic aggregate, melting the resulting mixture at a temperature which is 60° C. or more higher than the melting point of the resin, extruding the mixture, and applying an air bath. The method requires a high spinning temperature (as mentioned above, a temperature of 60° C. or more higher than the melting point of the polymer matrix) and the organic liquid used therein is a poor solvent of the polymer at room temperature. To improve water flux, a large amount of the organic liquid is a must, thereby worsening the spinnability of the mixture. Thus, the method is not so practicable.
A method for producing a hollow fiber membrane in the prior art includes mixing a polymer, a liquid insoluble to the polymer, and a polymeric pore forming agent with a surfactant, and then melting (at a temperature of 10-50° C. higher than the melting point of the polymer) and extruding the mixture to yield a hollow fiber membrane. To make the follow fiber membrane have permeable micropores, the liquid is washed using an organic solvent such as isopropyl alcohol and ethanol. The introduction of the organic solvent increases the production cost and even causes secondary pollution. Another method for producing a hollow fiber membrane includes mixing a polymer and a polymeric pore forming agent with a diluent, and then melting the mixture. Due to the compatibility difference of the water-soluble polymers used therein, for example, polyoxyethylene and polyvinylidene difluoride (PVDF), and the viscosity difference thereof at a spinning temperature, a uniform porous structure is very difficult to form. Thus, the comprehensive properties of the PVDF hollow fiber porous membrane decrease greatly.